When growing a film containing a metal element on a substrate, there is available an MOCVD (Metallo Organic Chemical Vapor Deposition) method using an organic metal gas. According to this method, when an organic metal to be used is a liquid, the organic metal formed into mist by a bubbling method is transported by a carrier gas to a reaction chamber. HVPE (Hydride Vapor Phase Epitaxy) is a method compared with MOCVD. According to this method, a metal is reacted with, for example, hydrogen chloride at a high temperature and is transported as a metallic chloride remaining at a high temperature to a substrate, thereby making the metallic chloride react with another gas on the heated substrate and growing a thin film of the compound. That is, HVPE allows a large amount of raw metal to be transported to a film growth reaction apparatus at a high speed, and hence can implement high-speed film growth.
The above method will be described by taking an example. A plate with Ga metal is placed in a heated quartz tube, and hydrogen chloride is let into the tube to produce Ga chloride (GaCl3). This Ga chloride is then transported to a downstream high-temperature portion while being kept at a high temperature (this transportation will be referred to as high-temperature transportation in this case). At the same time, when ammonia (NH3) is let into the same quartz tube, a GaN crystal grows on a substrate placed at the downstream high-temperature portion (see, for example, non-patent literature 1 and patent literature 1).
There is also available a method of melting a synthesized Ga chloride (GaCl3) at a temperature equal to or more than 78° C., bubbling it, and performing high-temperature transportation while keeping it at a temperature of about 130° C. (see, for example, patent literature 2). This HVPE reaction system has no organic material contained in a reaction gas, and hence can perform high-purity film deposition under wide temperature conditions. In addition, this method does not use a large amount of carrier gas, it is possible to achieve film growth at a speed 10 or more times higher than MOCVD using an organic metal as a raw material.
As a commercial-scale GaN crystal growth technique, MOCVD (Metallo Organic Chemical Vapor Deposition), which can transport a gas in a room-temperature region, is actually dominating the market as compared with HVPE. Assume that there are an apparatus or component (to be referred to as a solid gasification apparatus hereinafter) which produces a gas containing a material solid component by efficiently making a high-temperature gas contact a material solid, and an inexpensive, compact apparatus or component (to be referred to as a heated gas contacting apparatus hereinafter) which transports a produced gas while keeping it at a high temperature, and mixes the gas with another gas heated to a high temperature in another place so as to make them contact each other. In this case, the structure of the HVPE apparatus can be simplified.
Patent literature 3 discloses an invention relating to a solid gasification apparatus. The technique disclosed in patent literature 3 is an apparatus which produces a gas containing the element component of a solid by heating the solid and supplying a gas to it. This apparatus is configured to heat the solid itself by using a lamp, and has a large, complicated structure. In addition, the apparatus includes a mechanism which mechanically moves to open and close for the supply of a produced gas. This further complicates the structure. In practice, however, the structure is preferably reduced in size and simplified.
As described above, to simplify the structure of the solid gasification apparatus is a starting point of the present invention.
In this case, a compact, inexpensive solid gasification apparatus having a simplified structure can be applied to another industry, and hence is industrially important. If a solid is an organic material and a highly heated gas is superheated steam, the solid gasification apparatus produces methane gas (CH4) and hydrogen (H2). When a heated gas contacting apparatus makes 1,000° C. methane gas (CH4) contact 1,000° C. superheated steam, they react with each other to produce hydrogen and carbon dioxide gas. That is, the solid gasification apparatus is an apparatus for producing hydrogen and methane by decomposing an organic material, and hence can be used as a component of an apparatus or system designed to extract renewable energy from an organic material. That is, an apparatus designed to produce a gas by making a gas heated to a high temperature contact a solid is effective not only in the industrial field of HVPE but also in the industry of extracting renewable energy providing a huge market.
However, it is not easy to instantly heat a gas to a high temperature, and hence the conventional apparatus inevitably increases in size. More specifically, a conventional method in practical use is a method of producing a gas by inserting a material, which is to be heated to a high temperature, into a bundle of thin metal pipes, inductively heating the metal pipes, and transferring heat to the material through the metal pipes. This method is used as a method of producing steam of a high temperature of about 700° C. (which is sometimes called superheated steam). This apparatus is a large-sized apparatus with few square meters which is difficult to handle. Besides, it is expensive, costing several tens of millions of yen to several hundreds of millions of yen.
Another conventional method is to externally heat, by flame, a metal pipe into which a material to be heated is inserted. This method is a simple method, and hence has a long history of being used. However, the method has poor efficiency and requires a large-sized apparatus. In addition, the method has a drawback of inability to precisely control the temperature of a gas.
There has already been an invention (see, for example, patent literatures 4 and 5) relating to a compact apparatus which instantly produces a high-temperature gas by using a method different from these conventional methods. This invention relates to a heat exchange apparatus using the principle of instantly producing a high-temperature gas by letting a gas pass through a thin trench to produce a high-speed gas and making the gas collide with a metal wall heated to a high temperature. Using this apparatus as a component makes it possible to produce a gas containing a material element (solid gasification) by making a material solid and a high-temperature gas contact each other without increasing the apparatus size.